On-stream ore liberation detection system

ABSTRACT

A method for determining the extent to which ores should be crushed and ground for optimum beneficiation in which dust is separated from the crushed ore and is then continuously sampled, and concentrated as to the desired mineral component and the concentrate continuously analyzed to determine the content of one of the mineral components thereof. The analysis is then used to determine the extent of grinding to control the composition of the final concentrate. Also the analysis may be used to proportion ore obtained from various sources to assist in controlling the composition of the final concentrate.

United States Patent Williams [451 Apr. 25, 1972 OTHER PUBLICATIONSRiede, J. R, & Kachel G. C. Instrumentation and Automatic ControlSystems in Modern Processing Plants Canadian [72] Inventor: Charles J.Williams, Auroa, Minn. I

Mining Journal, pages 67- 72, Mar. i961. [73] Assignee: Erie DevelopmentCompany, Cleveland,

7 Ohm Primary Examiner-Donald G. Kelly [22] Filed; Nov. 19, 1969Attorney-Pierce, Scheffler & Parker [21] Appl. No.: 878,082 57 ABSTRACTA method for determining the extent to which ores should be if g 231/33crushed and ground for optimum beneficiation in which dust i 4 g isseparated from the crushed ore and is then continuously e 0 ea csampled, and concentrated as to the desired mineral com- [56] ReferencesCied ponent and the concentrate continuously analyzed to determine'thecontent of one of the mineral components thereof. UNITED STATES PATENTSThe analysis is then used to determine the extent of grinding to controlthe composition of the final concentrate. Also the g gahlstmm analysismay be used to proportion ore obtained from various Oren [3 x sources toassist in controlling the composition of the final concentrate.

9 Claims, 2 Drawing Figures HlNlNG FACE MINING FACE MINING FACE NO. lNO. 2 NO. 3

PRIMARY i CRUSHER MAGNETIC l CONCENTRATOR WASTE E 5 SECONDARY CRUSHERSILICA ANALYSER r J l l i l r "-1 l f I 9 E 10 1 1 l I l l ORE ROD BALLAGGLOMERATING BIN MILL HILL PELLETIZING PRODUCT V'PATENTEDAPRZS I972 3,658 26D SHEET 2 BF 2 DUST FROM 2 CRUSHERS l4 WATER SAMPLE -13 CUTTERMAGNETIC SEPARATOR WASTE I8 SILICA ANALYSIS INVENTOR. Y INN/H51 "J.[AK/'1 1 ////I/ C ON-STREAM ORE LIBERATION DETECTION SYSTEM Inbeneficiating low grade ores such as taconite, initially containing fromabout 20 to 55 percent iron mineral bearing material to a concentratecontaining from about 85 percent to about 100 percent iron oxide, it iscustomary to crush the ore in several stages and then grind it inseveral stages, removing gangue materials between the grinding stages.The removal of non-ferrous materials, including silica, is accomplishedby separators such as magnetic separators, hydrosizers, etc. Thus thefiner the ore is ground the greater is the extent of liberation andseparation of iron bearing minerals from the gangue material. The finaliron bearing material is agglomerated and pelletized for easy handlingand for shipping to furnace plants for smelting the ore to produce pigiron. For economic reasons it is impractical to grind the crushed ore toa fineness greater than that degree wherein valuable minerals aremechanically liberated from non-valuable minerals at which the finalproduct may contain about 85 to nearly 100 percent iron oxide. Thisgenerally is the economically desirable iron concentration for blastfurnaces. In order to produce pellets of higher concentration of iron,finer grinding would be required and this in turn increases cost so thatit is economically unfeasible.

Furnace operators now generally require pellets having a rather specificiron concentration in order to economically operate the furnaces.

During the mining of taconite ores, such as the ores found on the MesabiRange in Northern Minnesota, the ores at different locations are foundto vary somewhat in iron content so that it is desirable to know thesource of the iron ore in order to determine the necessary degree ofgrinding whereby the final pelletized product will have the desired ironconcentratron.

Usually samples of the ore are taken even before the ore is blasted outof the earth, by obtaining diamond drill core samples, which arephysically and chemically analysed. This method has one greatdisadvantage in that the core samples obtained represent only a verysmall part of the ore and are taken necessarily only at widely spacedintervals, thus giving a relatively poor representation of sampling, ofthe order of about 1 part in 8,600,000,000. In addition it is quitedifficult to obtain the core samples in the very hard taconite ores sothat diamond drilling techniques are usually required which areexpensive. The cuttings derived from the jet-piercing method for blasthole drilling, a process required because of the hardness of the ore,are not suitable for sampling the ores because of the high temperaturesinvolved which cause mineralogical changes in the ore particles.

Aside from the fact that the drill core samples do not provide asatisfactory sampling of the ore for mill control purposes there is theadditional disadvantage that the chemical analysis of such core samplesusually is representative of only a small volume of ore immediatelysurrounding the ore from which the sample was taken. The miningequipment usually progresses several tens of feet per day along a miningface containing broken ore having previously been blasted, and thediamond drill sample analyses are from holes drilled in the original orevarying distances from the mining face. Such samples are also subject tothe serious disadvantage that the chemical analysis of such samplesusually requires such a period of time that the ore from which thesample is taken has usually been ground to its ultimate fineness beforethe test results can be known. Thus the analysis results cannot be usedto control grinding of subsequent ores.

The present invention is designed to provide a sampling and analysisprocess by which a far more representative sample is obtained, i.e. ofthe order of 100,000 times more representative than the sample obtainedby diamond drill core sampling described above. Accordingly, the presentmethod involves cutting samples from all of the stream part of the timewhereas the diamond drill core method involves cutting samples from asmall part of the stream part of the time. By the present invention asample of about 15 to 25 pounds is obtained from about 700 to 800 longtons of ore and thus is a very much better sampling of the order ofabout 1 part in 80,000, and also the time for sampling and analysis issufiiciently short so that the results can be used not only forcontrolling the ultimate fineness of grind of the ore sampled but alsocan be used effectively to provide a control, even though somewhat lessprecise, for proportioning the original ores taken from different miningfaces so that the overall mixture when subjected to a relatively uniformfine grinding will result in a concentrate having the desired ironcontent. It will be understood therefore that the method of the presentinvention enables one to control the quality of product with muchgreater ease and certainty than has been possible heretofor.

In the usual process for beneficiating ores, the ore, after beingremoved from the mining face is crushed in several stages during whichtime the ore is reduced to particles ranging from a few microns to aboutan inch particles. At each stage of the crushing a great deal of dust isproduced and is removed from the ore stream by dust collectors, suctionmeans or the like. The crushed ore is subsequently passed to an ore binand then via a conventional mill line through a rod mill, magneticseparators, ball mill and other separators whereby the ore particles arereduced in size to the extent necessary for removal of most of theundesired silica and other gangue materials. Ore that is notsufficiently ground by the last ball mill may be recycled to the ballmill for regrinding. An example of the overall process and particularlya conventional mill line may be found in Mining Engineering, May 1963,pages 39 through 54, published by Society of Mining Engineers. It is thefinal grinding step which determines the ultimate iron concentration inthe final pellets and it is this iron concentration it is desired tocontrol.

As mentioned above during the crushing stages, dust is removed.According to the present invention it has been discovered that this dustmay be concentrated and the resulting concentrate analyzed for silicacontent and the analysis used to determine the extent of grindingnecessary in the ball mill in the last stages of grinding of the ore.Also this analysis may be used for determining the quantities of orederived from different mining faces to form the total ore mix to becrushed and delivered to the ore bins prior to being fed into a millline. In practical operations, such factors are of great advantage,since the desired fineness of grind is established before the ore orores are subjected to the grinding operations.

The discovery that the dust from the crushing steps may be recovered,concentrated and analyzed to determine the iron or silica content andthat this analysis may be directly correlated to the iron or silicacontent of the final product after the ore is processed into valuableconcentrate is the basis for the method of the present invention.

It was found, for example, that a direct relationship exists between themagnetically concentrated dust from the crusher and the concentrate of adiamond drill core sample Davis tube test. Various correlations werediscovered including the fact that the iron and silica analyses of eachscreen size fraction closely approximate that of the ore concentrateafter processing. It was further found that the silica analysis of thedust concentrate compared to the silica analysis of various millproducts, such as the rod mill feed tube test concentrate, finisherconcentrate tube test heads and finisher concentrate tube testconcentrate, showed a much higher degree of correlation than was foundbetween the diamond drill tube tests compared to the mill results.

The present invention is therefore a practical application of thediscovery of this high degree of correlation, together with thecontinuous supply of dust for sampling as well as the much morerepresentative nature of the samples compared to diamond drill tubetests.

The method of the present invention will now be described in greaterdetail with reference to the accompanying drawing, in which FIG. 1 showsa flow sheet of the overall beneficiating process and the location ofthe silica analyzer of crusher dust therein and FIG. 2 showsdiagrammatically the steps followed for sampling the dust and thecontrols derived therefrom.

According to FIG. 1, ore from different mining faces 1, 2 and 3 or moreis delivered to a series of crushers, of which two are illustrated at 4and 5. Dust from one or both of the crushers is slurried with water andthen passed to a concentrator 6 and the iron rich concentrate iscontinuously analyzed for silica as at 7. In the meantime the crushedore is moved to an ore bin 8 from whence it is passed via a conventionalmill line to grinders 9 and 10 and eventually to an agglomerating andpelletizing plant 11. As indicated by dotted lines the results of thesilica analysis at 7 may be used to control the one or more grindingoperations at 9 and/or 10 and/or may be used to control the relativequantities of ore supplied from one or the other of mining faces 1,2 and3.

In FIG. 2, the dust from one of the crushers is introduced into arotoclone 12 and is fed to a sample cutter 13 after having been slurriedwith water introduced at 14. The series of samples cut out from theslurried dust are continuously fed over a screen 15, such as a sievebend, to remove the small amount of larger tramp particles. The slurriedsamples are then fed to a magnetic separator 16, which may be a 3 drumlaboratory type of magnetic separator to form a concentrate. The wastematerial or gangue, i.e. non magnetic material is removed at 17. Thesamples of concentrate are then passed to a silica analyser 18 which maybe of any type, giving practically instantaneous results, eg anon-stream silica analyser of the x-ray type. It has been found howeverthat an on-stream analyser based on the neutron activation principle isparticularly suitable for this analysis. Analysers of this latter typeare described in the technical paper entitled Nuclear Techniques inOn-Stream Analysis of Ores and Coal" (ORO2980-l8) dated Sept. 26, 1968,by J.R..Rhodes, et al., Texas Nuclear Corporation, Austin,Texas,published by the U.S.Atomic Energy Commission, U.S.Dept. of Commerce,Bureau of Standards, and reproduced and distributed by Clearinghouse ofSpringfield,Va. 22151. An additional description appears in a technicalpaper entitled Neutron Activation Analysis for Industrial ProcessControl" by P.F.Berry and J.B. Ashe, Nuclear-Chicago Corporation, TexasNuclear Division, Austin, Texas, prepared for 4th Annual Symposium ofthe Instrument Society of America (Lake Superior Section), Duluth,Minn,June 19-29, 1969.

As used herein and in the appended claims the term onstream" as appliedto the analysis of the concentrated dust samples is intended to mean ananalysis the results of which are available for use substantiallyimmediately after the representative samples are taken from theconcentrated dust in a continuous or rapidly repetitive manner.

The results of the analysis determine the amount of silica in thesamples and these data can be directly correlated with the original orefrom which the sample was taken and therefore with the final ironcontent of the concentrate which is to be agglomerated and pelletized.For example, when a sample shows a high silica content it indicates theneed for giving the ore from which the sample was taken a finer grindthan samples showing a lower silica content. Furthermore, when thesample analysis shows such a high silica content that an excessiveamount of grinding would normally be required, it then becomes desirableand even necessary to select another source of the ore from those miningfaces where the iron content and physical characteristics of thecomposite ore are sufficiently favorable to eliminate the necessity forfiner grinding. Table I below gives a representative analysis of aconcentrate so produced from a dust sample and a representative analysisof a mill line concentrate. It is readily apparent that the ironcontents as well as the percent weights are quite comparable for theconcentrate from the dust sample and the mill concentrate. Some variancein iron content can be noted in the plus 200M fraction; however, this isto be expected because of the wide variance in size possible in thatcoarse fraction.

In the practice of beneficiating ores, it has become a well knownprinciple in the art of ore dressing that a direct relationship existsbetween requisite fineness of grind and desired TABLE I Concentrate fromdust 'Iyplcnl mill concentrate,

grade of concentrates produced therefrom, regardless of theconcentration process that is applied to treatment of the ores.

The process described heretofore applies specifically to treatment ofmagnetic taconite ores. Said process is in universal commercial usethroughout the world.

Treatment of other than magnetic taconite ores has similar principles inthat the ores must be crushed, ground and concentrated by some processsuch as various gravity processes and the well known flotation processused to produce the bulk of the worlds supply of lead, zinc, copper andothers. Most metallic and non-metallic minerals, contained in ores aretreated by similar principles of the art of ore dressing.

In the treatment of all ores there exists, as is well known to those whopractice the art, certain common problems. One problem is the requisitefineness of grind to produce a finished concentrate of specified grade.It will be understood that too coarse a grind can produce a concentratethat will chemically analyze low in desired valuable mineral content dueto incomplete liberation of valuable and non-valuable mineralconstituents. Contrarily, ores may be ground too fine, wherein the gradeof produced concentrate may be obtained at the expense and high cost ofovergrinding. Also, extreme overgrinding can readily reduce the desiredvaluable mineral constituents to so fine a size that the mineralparticles will not respond to the principle of the concentration processin use, and is thus lost and passes out with the rejected non-valuableconstituent of the ore.

A second problem common to treatment of all ores is that of blending.Most concentration processes are generally based on treating ores ofuniform or average values, both as to the valuable and non-valuablemineral constituents. Unifonnity is generally considered both fromphysical and chemical viewpoints. However, nature did not produce oredepositions of unifonn stylized types. Thus, in mining of ore deposits,considerable efforts are devoted and much monies expended to produceores from various mining faces at any single mining venture that tend toprovide the mill or concentrator at that mining property with a blendedore having more or less uniform character.

Thus the subject of this invention is generally directed to thetreatment of any and all ores requiring ore dressing treatment forproduction of concentrates. For instance, the invention could readily beused at a copper porphyry mining operation by merely substituting aflotation machine in place of the magnetic separator and analyzing theflotation concentrate thus produced for its copper content. Likewise, intreating certain types of hematitic ores, gravity concentration unitssuch as shaking tables or jigs could be used as the concentrating deviceand the resultant concentrate analyzed for either its iron or siliceouscontent.

The subject of this invention is further directed to the treatment ofores and like materials by means of dry processing, such as for example,treatment of ores by means of dry electrostatic concentration methodswhich processes are commonly applied in the treatment of specularhematitic ores, ilmenite and rutile ores, et cetera. All dryconcentration processes are included in the broader aspects of thepresent invention.

In such processes where dry concentration methods are used, theinvention is used in a like manner to that employed where wetconcentration methods are used. Thus the dust is collected, sampled andfed to a dry concentration unit and the dry concentrate is subjected toanalysis in a dry fonn. The dry form may consist of the concentratedsolids suspended in an air stream, or they may be briquetted or preparedin a suitable disc form, or in any other manner in common use.

It is, therefore, to be understood that the invention as described indetail herein, may be applied not only to the treatment of slurries inthe wet manner but also to treatment of dry materials in a dry manner,or, in any combination thereof.

Although the process has been described with particular reference to thesilica analysis of dust from crushers employed in beneficiating taconiteores, it will be understood that the process is equally applicable toother magnetic ores and even to non-magnetic ores where other means areused for concentrating same, such as flotation and gravity concentrationprocesses. Thus, it is applicable to non-ferrous ores as well.

I claim:

1. In the beneficiation of ores in which an ore is crushed and thenground for separating gangue materials from a wanted mineral, the methodof controlling the degree of fineness of grinding to produce the desiredconcentrate comprising continuously separating dust from the crushedore, concentrating said separated dust for the content of wantedmineral, continuously analyzing said concentrated dust for one of themineral components thereof and controlling the degree of grinding inaccordance with the analysis for the mineral component whereby the finalground product has the desired concentration of wanted mineral.

2. The method as claimed in claim 1 wherein the concen trated materialis analyzed for silica content.

3. The method as claimed in claim 1 and further comprising forming anaqueous slurry of the dust separated from the crushed ore beforeconcentrating said separated material for the content of wanted mineral.

4. The method as claimed in claim 1 and further comprising cutting acontinuous series of samples of said dust prior to concentrating saidsamples of said material.

5. The method as claimed in claim 1 and further comprising initiallycombining ore from at least two sources, the approximate composition ofeach of said at least two sources being known, in such proportion asindicated by said analysis that the wanted mineral of the final productwill be substantially as desired.

6. The method as claimed in claim 1 wherein the fineness of grinding isincreased as the gangue content of the analyzed concentrated dustincreases.

7. The method as claimed in claim 1 wherein the fineness of grinding isdecreased as the gangue content of the analyzed concentrated dustdecreases.

8. The method as claimed in claim 1 wherein said concentrated dust isanalyzed for the mineral component by the neutron activation principle.

9. The method as claimed in claim 1 wherein said concentrated dust isanalyzed by an on-stream method of analysis which provides substantiallyinstantaneous results.

2. The method as claimed in claim 1 wherein the concentrated material isanalyzed for silica content.
 3. The method as claimed in claim 1 andfurther comprising forming an aqueous slurry of the dust separated fromthe crushed ore before concentrating said separated material for thecontent of wanted mineral.
 4. The method as claimed in claim 1 andfurther comprising cutting a continuous series of samples of said dustprior to concentrating said samples of said material.
 5. The method asclaimed in claim 1 and further comprising initially combining ore fromat least two sources, the approximate composition of each of said atleast two sources being known, in such proportion as indicated by saidanalysis that the wanted mineral of the final product will besubstantially as desired.
 6. The method as claimed in claim 1 whereinthe fineness of grinding is increased as the gangue content of theanalyzed concentrated dust increases.
 7. The method as claimed in claim1 wherein the fineness of grinding is decreased as the gangue content ofthe analyzed concentrated dust decreases.
 8. The method as claimed inclaim 1 wherein said concentrated dust is analyzed for the mineralcomponent by the neutron activation principle.
 9. The method as claimedin claim 1 wherein said concentrated dust is analyzed by an on-streammethod of analysis which provides substantially instantaneous results.